These units are pretty easy to find. In addition to online, auto parts stores, WalMart, kmart, etc., all carry them in various sizes.
The unit I have has a couple of cables that I can choose from to connect to my 12v source. I can use the cigarette lighter adapter cable or a cable with clamps. During a power failure last year that lasted several days I used it to charge my cell phone and laptop batteries. I'll never be without one again.